RESEARCH ON GEM FELDSPAR FROM THE SHIGATSE REGION OF TIBET Ahmadjan Abduriyim, Shane F. McClure, George R. Rossman, Thanong Leelawatanasuk, Richard W. Hughes, Brendan M. Laurs, Ren Lu, Flavie Isatelle, Kenneth Scarratt, Emily V. Dubinsky, Troy R. Douthit, and John L. Emmett The existence of a natural red andesine deposit in China/Tibet has been the subject of controversy since 2006. In late September 2010, an international group traveled to the Shigatse region of Tibet and visited two reported andesine occurrences, at Zha Lin village and the Yu Lin Gu alluvial fan. These sites are located ~3 km from the previously investigated Bainang andesine mining area near Nai Sa village. The Zha Lin deposit appeared genuine, but the group could not confirm the authen- ticity of the Yu Lin Gu occurrence, and no primary andesine-bearing source rocks were found in either area. Some of the samples had glassy surface residues that are difficult to explain naturally, while initial argon isotopic measurements of a few Zha Lin and Yu Lin Gu andesines (without glassy residues) showed that they had not been heated. Laboratory studies of the Tibetan samples—and a comparison to known-treated red andesine from Inner Mongolia—showed that it may be possible to separate these feldspars using a combination of several advanced destructive techniques, but this methodology is not practical for gem testing laboratories. More detailed investigations will be needed to establish feasible identification criteria for natural-color andesine from Tibet. opper-bearing red to green plagioclase feldspar copper was being diffused into andesine in China of gem quality has been known from Oregon and Thailand by a multi-step heating process for decades (e.g., Johnston et al., 1991). In (Furuya, 2008; Milisenda et al., 2008). While this was C apparently being performed on an experimental basis 2002, a new gem plagioclase appeared on the market, allegedly from the Democratic Republic of the in Thailand, commercial treatment was reportedly Congo (Fritsch, 2002; Krzemnicki, 2004; here taking place in China by a professor in Xi’an (Lang, referred to as the Congo), and similar material 2002). The starting material was alleged to be pale appeared in 2005 that was represented as being from yellow andesine from Guyang County, Inner Tibet (see, e.g., figure 1 and Laurs, 2005). Chemical Mongolia, China. Suspicions about the authenticity analysis of red feld spars reportedly from Tibet (an of the “Chinese red feldspar” on the market circulat- autonomous region of China) and the Congo showed ed on the Internet and elsewhere (e.g., Furuya, 2008; that they fall near the border of the andesine- James, 2008). labradorite compositional range (Abduriyim, 2009b; To address whether natural red andesine occurs Rossman, 2011); for simplicity, this material will be in Tibet, in 2008 one of the authors (AA) and five referred to as andesine in this article. gem dealers and a gemologist visited an alleged Reports published in 2008 showed evidence that deposit called Bainang (or Bai Lang), located near Nai Sa village ~55 km southeast of Shigatse (or Xigazê; see figure 2; Abduriyim, 2008, 2009a,b). The visit See end of article for About the Authors and Acknowledgments. was organized by Chinese miner Li Tong (Tibet GEMS & GEMOLOGY, Vol. 47, No. 2, pp. 167–180. Andesine, Shenzhen, China). Author AA also visited © 2011 Gemological Institute of America two deposits of pale yellow andesine in Inner ANDESINE FROM TIBET GEMS & GEMOLOGY SUMMER 2011 167 Figure 1. These andesines (6.71–15.51 ct) were represented as untreated (natural color) stones from Tibet. Courtesy of Do Win Development Co. Ltd.; photo by Robert Weldon. Mongolia (Shui Quan and Hai Bou Zi, both in GemResearch Swisslab (GRS, Lucerne, Switzerland) Guyang County), and samples were collected at each and in 2010 by China’s National Gemstone Testing locality. In addition, he attempted to contact the Center (NGTC, Beijing). Dr. Adolf Peretti from GRS Chinese treater in Xi’an, who was unwilling to meet was taken by Li Tong to a Tibetan deposit located with him. hundreds of kilometers away from the site of AA’s The internal features and chemical composition 2008 Tibet trip (again, see figure 2), but Peretti con- of the Tibetan samples collected on the 2008 expedi- cluded the occurrence was fake (Fontaine et al., tion were found to closely resemble the allegedly 2010). On two expeditions in May and August 2010, copper-diffused Inner Mongolian red andesine on the teams from NGTC collected andesine samples from market, to the degree that doubt was cast on the nat- a reported deposit near Zha Lin village and at the ural origin of the Tibetan stones (Hughes, 2010; Nai Sa–Bainang mine. They believed that these sites Rossman, 2011). were probably “salted,” but that the question could In an effort to resolve the controversy, other field only be truly answered with a full geologic survey of trips to Tibet were carried out in 2009 by the area (Wang et al., 2011). Yarlung River G 318 CHINA Shigatse Figure 2. The reported andesine mines visited S 204 by Abduriyim’s 2010 expedition are located in Bainang Zha Lin town 1 Nai Sa south-central Tibet, ~55 Reported andesine 2 TIBET AUTONOMOUS REGION occurences 3 km from Shigatse. Also 1 Zha Lin shown is another report- 2 Yu Lin Gu 3 Nai Sa–Bainang 0 15 km ed andesine occurrence in Tibet (Gyaca) that Lhasa Fontaine et al. (2010) ✪ Shigatse Gyaca determined was fake. The inset NEPAL shows the locations of the report- Andesine Mt. Everest INDIA ed Zha Lin, Yu Lin Gu, and Nai ✪ INDIA im Sa–Bainang andesine localities in Kathmandu k BHUTAN Sik Tibet. 0400 kmN MYANMAR BANGLADESH 168 ANDESINE FROM TIBET GEMS & GEMOLOGY SUMMER 2011 In late September 2010, another party visited GIA website (www.gia.edu/research-resources/news- Tibet that included authors AA, BML, RWH, TL, FI, from-research/index.html). Although the andesine and Young Sze Man of Jewellery News Asia. Accom - controversy is still not resolved, it is hoped that this panying them were Christina Iu (M. P. Gem Corp., article will provide a foundation for others who wish Yamanashi, Japan), Li Tong and his wife, and He to pursue further studies of this material. Qung (an employee of Mr. Tong’s). They studied the reported andesine occurrence at Zha Lin village, as LOCATION AND ACCESS well as an additional locality called Yu Lin Gu With the exception of the occurrence visited by Dr. (Abduriyim and Laurs, 2010; Abduriyim et al., 2010; Peretti, the reported andesine deposits are located in Bainang County, ~55 km southeast of the region’s second largest city, Shigatse (or Xigazê), in southern Tibet (figure 2 and table 1). All three localities (Nai NEED TO KNOW Sa–Bainang, Zha Lin, and Yu Lin Gu) are situated within 2–3 km of one another. They are located ~8 • At Zha Lin and Yu Lin Gu in southern Tibet, andesine pebbles are hosted by alluvial sedi- km southeast of Bainang town, near the villages of ments, as at the nearby Nai Sa–Bainang occurence. Zha Lin (Zha Lin and Yu Lin Gu localities) and Nai • Samples from all three localities showed over- Sa (Bainang mine). lapping gemological and chemical properties, From the capital city of Lhasa, it takes more than except for traces of Ag in Yu Lin Gu andesine. five hours to drive ~300 km to Shigatse on a paved • Some of the samples had glassy surface residues, road that crosses two passes at 4,900 and 5,088 m. while initial argon isotopic measurements of From Shigatse, it takes another 1 –2 hours to drive to pieces from Zha Lin and Yu Lin Gu (without the mining area on mostly paved roads. Foreigners glassy residues) showed no evidence of signifi- are forbidden from visiting this area without autho- cant heating. rization from both the Chinese government and • No reliable and practical methodology was local authorities. found for separating these feldspars from known- treated red andesine from Inner Mongolia. GEOLOGIC SETTING The andesine is hosted by alluvial sediments weath- ered from sedimentary formations consisting mainly of shale and clay-rich sandstone. These were Hughes, 2010; Leelawatanasuk, 2010). These areas described as Tertiary on a geologic map published by are located ~3 km from the Nai Sa–Bainang mining the Chinese government (“Qin Zang Gao Yuan...,” area that AA visited in 2008. Due to the objection of 2005), while Guilmette (2008) indicated that the sed- a local monk who controls access to the land in this imentary formations in this area are much older area, the party was unable to visit the Bainang mine. (Late Triassic). Mechanical weathering of these According to villagers interviewed by the expedition, rocks created alluvial fans and stream-deposited the orange-red stones have been known in this gravels that locally contain pebbles of the andesine. region of Tibet for several decades or longer. No original host rocks for Tibetan andesine were This article reviews the geologic field informa- found during any of the field studies mentioned tion gathered by the expedition group and briefly summarizes results of laboratory work on the sam- ples they collected, including their gemological prop- TABLE 1. Reported andesine deposits in Tibet. erties, surface features, chemical and isotopic com- Site Coordinates position, and structural order as revealed by powder a X-ray diffraction. In addition, this study gives obser- Bainang (South) 29°02.57’N, 89°22.17’E; 4,072 m (13,360 ft.) Bainang (North) 29°02.71’N, 89°22.18’E; 4,049 m (13,285 ft.)a vations of “matrix” specimens that were supplied Zha Lin 29°03.95’N, 89°20.88’E; 3,929 m (12,891 ft.) through Li Tong, and also reports some initial exper- Yu Lin Gu 29°03.08’N, 89°20.76’E; 4,102 m (13,460 ft.) iments that investigated the diffusion of silver into Gyaca (Jia Cha) 29°08.07’N, 92°35.95’E; 3,400 m (11,155 ft.) andesine (since this element was detected in sam- County, Shan ples from the Yu Lin Gu occurrence).